1. Field of the Invention
This invention relates to a photoresist stripping solution and a method of stripping photoresists using the same. More particularly, it relates to a photoresist stripping solution which is excellent in protecting both Al— and Cu-based wiring conductors and other metal conductors from corrosion and in stripping photoresist films and post-ashing residues; and a method of photoresists using the same. The present invention is suitable for use in the fabrication of semiconductor devices such as ICs and LSIs, as well as liquid-crystal panel apparatus.
2. Description of Relevant Art
The fabrication of semiconductor devices such as ICs and LSIs, as well as liquid-crystal panel apparatus, comprises forming a uniform photoresist coating over conductive metallic layers, insulation layers such as an SiO2 film formed on a substrate (silicon wafer) by CVD; performing selective exposure and development to form a photoresist pattern; selectively etching the substrate having the conductive metallic layers, the insulation layers formed thereon using the photoresist pattern as a mask to thereby form a microcircuit; and then removing the unwanted photoresist layer with a stripping solution. For removal of such unwanted photoresist layers, various organic stripping solutions has been used from safety and strippability standpoints.
Examples of the conductive metallic layers formed by CVD as described above include those of aluminum (Al); aluminum alloys (Al alloys) such as aluminum-silicon (Al—Si), aluminum copper (Al—Cu) and aluminum-silicon-copper (Al—Si—Cu); titanium (Ti); titanium alloys (Ti alloys) such as titanium nitride (TiN) and titanium-tungsten (TiW); tantalum (Ta), tantalum nitride (TaN), tungsten (W), tungsten nitride (WN) and copper (Cu). These conductive metallic films are formed in one or more layers on the substrate. In recent years, both of devices having Al-based conductors (Al and Al alloy-based wirings) and devices having Cu-based conductors are coexisted. Accordingly, it has been required to protect both of these two types of devices from corrosion with the use of a single photoresist stripping solution.
Furthermore, with the recent tendency toward highly integrated, high-density circuits, dry etching enabling fine etching with a higher density has become the major means. Also, it has been a practice to employ plasma ashing to remove the unwanted photoresist layers remaining after etching. After these etching and ashing treatments, residues comprising modified photoresist films and other components that are referred to horn-like shaped “veil”, “fences” or “side-walls” remain on the bottom or side wall of patterned grooves. In case of forming a pattern on a substrate having an Si-based interlayer film, such as an Si-based insulation film (SiN film, SiO2 film, etc.) and a low dielectric film (SOG film, etc.), Si-based residues (Si-based depositions) are sometimes formed around pattern hole openings. In addition, etching of metallic layers and ashing treatment builds up metal depositions. Such post-ashing residues or depositions should be completely stripped away so as to keep good yields in the fabrication of semiconductors.
In recent years, further highly-density and highly-integrated substrates are needed, and thus the treating conditions in the etching and ashing steps become more and more strict. As a result, it is also urgently required to achieve improved corrosion resistance of metal wirings as well as improved residue-strippability of stripping solutions, compared with conventional ones.
Under these circumstances, there have been frequently employed stripping solutions for photoresists and post-ashing residues which contain amines or hydrofluoric acid as the main component. Among all, those containing hydrofluoric acid as the main component show excellent strippability especially for post-ashing residues.
Examples of stripping solutions containing hydrofluoric acid as the main component include: a resist stripping solution composition of pH 5-8 containing a salt of hydrofluoric acid with a base free from metal ions, a water-soluble organic solvent and water optionally together with a corrosion inhibitor (JP-A-9-197681); and a cleaner for semiconductor devices containing a quaternary ammonium salt and a fluorine compound, and further adding a water-soluble organic solvent (JP-A-7-201794).
The resist stripping solution composition in JP-A-9-197681 is to a certain extent effective in strippability and antiorrosivity on semiconductor devices having Al wiring conductors, however, it fails to exert any satisfactory effect of protecting devices having Cu wiring conductors from corrosion.
In the cleaner in JP-A-7-201794, tetramethylammonium formate and trimethyl(2-hydroxyethyl)ammonium salt are used as the quaternary ammonium salt. Although the corrosion of Cu wiring conductors can be relieved to a certain extent by using these compounds, there arises another problem that strippability for Cu-based metallic depositions (residues) is still insufficient.
JP-A-2000-273666 teaches a cleaner solution containing a sulfur-based corrosion inhibitor for protecting Cu wiring conductors from corrosion. However, any satisfactory strippability for Cu-based metallic depositions (residues) also cannot be established by using this cleaner solution.
As discussed above, none of the conventional photoresist stripping solutions can satisfy both of the requirements for efficient strippability and effective inhibition of metal corrosion. This is because strippability offsets the performance of inhibiting corrosion in a photoresist stripping solution. That is to say, there is a problem that one of the above-described requirement cannot be fulfilled unless the other is sacrificed. In the ultrafine processing employed in these days, in particular, the strippability for photoresist films and post-ashing residues should be further improved and it is therefore needed to enhance the effect of protecting metal wirings from corrosion. Recent models of semiconductor devices can be divided into two type, one using Al wiring conductors (Al, Al alloy and other Al-based metal wiring) and the other using Cu wiring conductors (Cu-based metal wiring). In addition to the need to protect devices of these two types from corrosion with the use of a single stripping solution, it is also required to provide effective protection against corrosion of other metals on the devices. Further improvements are desired to achieve effective stripping away of photoresists and post-ashing residues and to protect metal conductors from corrosion.